flak monkey
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| posted on 25/8/09 at 12:11 PM |
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Another supercharger thread from me
Basically after some info from those who have been there and done it.
I will either later this winter or next, be fitting a rotrex supercharger to the Duratec.... so I need to clarify a few points.
I am going to be running 0.9bar boost on std compression ratio (albeit forged) internals. This is a proven set up as used on the 320bhp Caterham
X330.
What I would like to do, is run a slightly undersize pulley so I can get the boost on earlier and then vent the excess as the rpms increase, gving a
smoother power curve and also more power lower down the revs. So basically I am looking for a wastegate type solution, only for a supercharger. Anyone
know of anything suitable, or has done it?
Or would you not bother and just size the pulley correctly in the first place?
I know that I will need a bypass valve to vent the boost on overrun and at cruising for better economy. So I need to source one of those too.
Hopefully someone can help 
Cheers,
David
Sera
http://www.motosera.com
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Mr Whippy
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| posted on 25/8/09 at 12:20 PM |
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I thought the whole point of a supercharger was that the boost was there all the time, right from idle? What makes you think you'll be getting a
lower pressure at low rev's? Given that your cam will be the real limit to when the engine picks up and that's already several thousand
rpm is it worth wasting so much energy dumping unused air at more usable engine speeds? I'd also imagine it would sound like a hissing steam
train all the time, which might get a bit annoying 
[Edited on 25/8/09 by Mr Whippy]
Fame is when your old car is plastered all over the internet
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graememk
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| posted on 25/8/09 at 12:29 PM |
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i dont know about tried and tested, did Caterham make many X330's ?
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flak monkey
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| posted on 25/8/09 at 12:29 PM |
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quote:
Originally posted by graememk
i dont know about tried and tested, did Caterham make many X330's ?
Umm well no, only 1 i think, but at it worked at least
David 
Sera
http://www.motosera.com
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graememk
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| posted on 25/8/09 at 12:35 PM |
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i was under the impression you could get the duracell engine up to 250 bhp with a few internal mods anyway how much bhp do you need ?
Rods, Pistons, Head, cams, uprated bearings to make it last, steel fly wheel etc etc
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flak monkey
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| posted on 25/8/09 at 12:35 PM |
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quote:
Originally posted by Mr Whippy
I thought the whole point of a supercharger was that the boost was there all the time, right from idle?
The boost builds as revs rise. So max boost is set for when you are at mox revs.
But if you can get max boost lower down you should be able to make more power....
Sera
http://www.motosera.com
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Ivan
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| posted on 25/8/09 at 01:13 PM |
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Hi David - surely traction will be a major problem for you - so is early boost such a good thing - in the corners your revs should be in the right
place to benefit from boost anyway so the only place early boost is possibly beneficial is from a standing start - and then you will be traction
limited anyway.
I would stick with the standard pulley - I think blow off valves are just something more to cause problems and are difficult to get working right
without creep which will negate some of their effectiveness. If you set the start of the opening at the maximum pressure then you will get some
overboost putting your motor at risk (also if they stick closed) and if you set them to be part open at max pressure then you have boost creep
problems with it taking longer than it should to reach max boost and also have wasted energy causing increased charge temperatures..
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Dangle_kt
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| posted on 25/8/09 at 01:27 PM |
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Is having power lower down the rev range a good idea in such a light car? Is it not better to follow a more well trodden path, it's not like you
fall over superchwrhed duratec engines every week.
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Ivan
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| posted on 25/8/09 at 01:35 PM |
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Something I forgot in my reply above - in a vehicle you don't feel acceleration - you only feel a change in acceleration (just like you
don't feel gravity - only a change in gravity as when a lift starts or stops).
So ever increasing boost will impress you and your passengers much more than early boost peak with a plateau for the last few thousand revs.
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BenB
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| posted on 25/8/09 at 01:45 PM |
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What type of blower are you going for? If you go centrifugal you won't have much boost at low pressure anyway. If you go Roots you probably
equally don't want to spin it too fast otherwise you'll lose efficiency...
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flak monkey
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| posted on 25/8/09 at 01:58 PM |
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Cheers chaps, good advice, keep it coming.
I will be using a C30-95 Rotrex supercharger Its about the only one that will fit I think.
Sera
http://www.motosera.com
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MikeRJ
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| posted on 25/8/09 at 02:59 PM |
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quote:
Originally posted by Mr Whippy
I thought the whole point of a supercharger was that the boost was there all the time, right from idle?
The Rotrex is a centrifugal blower, basically a mechanically driven (rather than exhaust driven) turbo, so boost is RPM dependant.
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Stuart_B
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| posted on 25/8/09 at 05:55 PM |
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that is teh same supercharger, i am looking, at but for not this winter next winter, when i am 19, i think my insurance will be ok with it.lol
stuart
black mk indy, 1.6pinto on cbr600 bike carb's.
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sebastiaan
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| posted on 25/8/09 at 06:13 PM |
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I'd keep the boost low at low revs, since the engine (with stock CR!) will be more prone to detonation at lower engine speeds.
Also, using a blow-off valve at high engine speeds seems a waste of compressed air and will significantly increase fuel consumption at that engine
operating point (but that's probably of less concern to you ;-)) and will make the entire setup significantly more complex.
If you really want low end grunt, fit a positive displacement supercharger.
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widz
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| posted on 25/8/09 at 06:58 PM |
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scootz has a rotrex kit for sale on here
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jpindy3
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| posted on 25/8/09 at 07:53 PM |
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turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more
with a turbo,ie more boost
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flak monkey
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| posted on 25/8/09 at 08:20 PM |
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quote:
Originally posted by jpindy3
turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more
with a turbo,ie more boost
Um, wrong, wrong, wrong and wrong.
Neither is more reliable than the other. If anything i would say turbos are a little less reliable.
Supercharged engines perform MUCH better lower in the rev range as there is no lag before they come on boost. Its all a smooth power delivery. If you
reatin stock CR as well your low down driveability is totally unaffected.
Fuel consumption, probably not much in it.
And you can run just as much boost with a SC as you can with a turbo.
David
Sera
http://www.motosera.com
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jpindy3
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| posted on 25/8/09 at 09:32 PM |
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turbo it
there is alot more to go wrong with a charger than a turbo,more macanical.
[Edited on 25/8/09 by jpindy3]
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Ivan
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| posted on 26/8/09 at 07:11 AM |
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I am a big fan of turbo's but as always there are compromises, a small lowish pressure turbo is most likely lighter than a supercharger (a good
thing) - will reach full boost quicker and earlier than a supercharger (a good thing) - is not very linear in boost (a bad thing) - boost is not rev
proportional (a bad thing) - might be more efficient - a good thing.
I think that overall a supercharger might give better control of power delivery on the track at the cost of more mechanical complexity and maybe
weight and maybe thermal efficiency.
I think that most of the so called negative aspects of both can largely be corrected by the proper selection of the right unit.
I know that most people (including many so called experts) fit the most readily available turbos that might not be ideally matched to the air flow
requirements of the application. Care taken to ensure an ideally matched turbine and compressor housings with the right nozzle sizes and trim levels
will provide a turbo that will minimise lag.
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jpindy3
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| posted on 27/8/09 at 07:54 AM |
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quote:
Originally posted by flak monkey
quote:
Originally posted by jpindy3
turbo it there so much better than superchargers,more relyable better on fuel when around town or driving lower down the range,also you can tune more
with a turbo,ie more boost
Um, wrong, wrong, wrong and wrong.
Neither is more reliable than the other. If anything i would say turbos are a little less reliable.
Supercharged engines perform MUCH better lower in the rev range as there is no lag before they come on boost. Its all a smooth power delivery. If you
reatin stock CR as well your low down driveability is totally unaffected.
Fuel consumption, probably not much in it.
And you can run just as much boost with a SC as you can with a turbo.
David
so what happens when you want more power,
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flak monkey
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| posted on 27/8/09 at 08:19 AM |
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quote:
Originally posted by jpindy3
so what happens when you want more power,
Same thing you do with a turboed engine, up the boost. Smaller SC pulley and remap and away you go. More or less, theres always a limit on how far you
can go before detonation becomes an issue though.
TBH I dont think I will want more than 320bhp in a seven.... and I reckon I will have trouble putting that much down 
Sera
http://www.motosera.com
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alistairolsen
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| posted on 27/8/09 at 08:45 AM |
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quote:
Originally posted by Ivan
Something I forgot in my reply above - in a vehicle you don't feel acceleration - you only feel a change in acceleration (just like you
don't feel gravity - only a change in gravity as when a lift starts or stops).
So ever increasing boost will impress you and your passengers much more than early boost peak with a plateau for the last few thousand revs.
I dont think thats right... You feel the change in speed as the lift starts and stops, but not the constant speed while its in motion. Same as you
feel a push from an aeroplane as it accelerates but nothing in flight. in your average car, the acceleration rate reduces as speed increases due to
air resistance and rolling drag, but you can still feel acceleration.
jounce, or rate of change of acceleration is of course important, and one of the prime factors in rollercoaster design. I Just dont think its the only
one!
My Build Thread
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alistairolsen
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| posted on 27/8/09 at 08:47 AM |
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quote:
Originally posted by flak monkey
quote:
Originally posted by jpindy3
so what happens when you want more power,
Same thing you do with a turboed engine, up the boost. Smaller SC pulley and remap and away you go. More or less, theres always a limit on how far you
can go before detonation becomes an issue though.
TBH I dont think I will want more than 320bhp in a seven.... and I reckon I will have trouble putting that much down
except if you chose correctly and geared correctly to start with you will have the cnages the supercharger to go any further. In the same way if you
spec a turbo correctly you cannot tune the engine more without changing it.
This concept of turbo being "tuneable" is only because manufacturers tend to fit something slightly larger than needed in the name of 150k
miles relliability and hence a "stage1" chip will generally net a 40% power increase. In reality it is after this chip that the turbo is
specced correctly for the engine!
My Build Thread
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